U.S. patent number 6,932,458 [Application Number 10/303,443] was granted by the patent office on 2005-08-23 for obtaining high frequency performance by controlling chamber pressure.
This patent grant is currently assigned to Ricoh Printing Systems America, Inc.. Invention is credited to Stuart D. Howkins, Charles A. Willus.
United States Patent |
6,932,458 |
Howkins , et al. |
August 23, 2005 |
Obtaining high frequency performance by controlling chamber
pressure
Abstract
A method and apparatus to prevent ink starvation includes
keeping ink in a primary common reservoir at a high pressure. The
ink is transferred from the primary common reservoir to a local
reservoir when a pressure drop across a restrictor decreases
pressure in the local reservoir. The pressure drop across a
restrictor results from a higher ink flow rate due to rapid firing
of the transducer.
Inventors: |
Howkins; Stuart D. (Ridgefield,
CT), Willus; Charles A. (Newtown, CT) |
Assignee: |
Ricoh Printing Systems America,
Inc. (Simi Valley, CA)
|
Family
ID: |
32325008 |
Appl.
No.: |
10/303,443 |
Filed: |
November 25, 2002 |
Current U.S.
Class: |
347/47 |
Current CPC
Class: |
B41J
2/14201 (20130101); B33Y 30/00 (20141201); B41J
2/17556 (20130101); B41J 2002/14419 (20130101) |
Current International
Class: |
B41J
2/14 (20060101); B41J 2/175 (20060101); B41J
002/16 () |
Field of
Search: |
;347/47,44,42,41,40,29,26,20,9,7,5,68,69,70,71,72 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Gordon; Raquel Y.
Attorney, Agent or Firm: Pillsbury Winthrop Shaw Pittman
LLP
Claims
What is claimed is:
1. An ink-jet print head, comprising: a local reservoir to receive
ink from a primary common reservoir, wherein the primary common
reservoir keeps the ink at a high hydrostatic pressure; a
restrictor passage to receive the ink from the local reservoir to
and transfer the ink; an ink let chamber to receive the ink from
restrictor passoge, said ink let chamber inclding an ink droplet
ejection orifice; an election device to elect the ink through the
ink droplet ejection orifice; and a pressure sensor located in the
ink jet chamber to measure pressure within the ink jet chamber
during firing of the election device and to transmit a signal.
2. The ink jet print head of claim 1, further including a
controller to receive the signal from the pressure sensor and to
transmit a valve signal.
3. The ink jet print head of claim 2, further including a valve to
allow an increase hydrostatic pressure in the local reservoir,
wherein the valve receives the valve signal from the controller and
the valve opens during rapid firing of the ejection device during
printer operation.
4. The ink jet print head of claim 3, further including a bleed
valve coupled to the controller to dissipate pressure from the
local reservoir and ink jet chamber, wherein the bleed valve
receives the valve signal from the controller and the bleed valve
opens when the pressure in the ink jet chamber is too high.
5. The ink jet print head of claim 4, wherein excess pressure
dissipated by the bleed valve is transferred to the primary common
reservoir.
6. The ink jet print head of claim 4, wherein the valve and the
bleed valve are located in one physical valve device.
7. The ink jet print head of claim 1, wherein the primary common
reservoir is kept at the high hydrostatic pressure by applying air
above the ink by a pressure applying device.
8. The ink jet print head of claim 1, further including a pressure
sensor to measure pressure in the local reservoir and a transducer
firing rate determiner to identify a firing rate of the transducer,
wherein the pressure sensor outputs a signal and the transducer
firing determiner outputs a rate signal.
9. The ink jet print head of claim 8, further including a
controller to receive the signal from the pressure sensor and the
rate signal from the transducer firing rate determiner, to compute
the pressure in the ink jet chamber, and to output a valve signal
to a valve to open if the pressure is low in the ink jet
chamber.
10. The ink jet print head of claim 8, further including a
controller to receive the signal from the pressure sensor and the
rate signal from the transducer firing rate determiner, to compute
the pressure in the ink jet chamber, and to output a valve signal
to a bleed valve to open if the pressure is high in the ink jet
chamber.
11. The ink jet print head of claim 1, further including: a
controller to receive the signal and to transmit a displacement
signal, and a displacement device to receive the displacement
signal and to displace the local reservoir in or out via a
diaphragm to increase or reduce pressure in the local
reservoir.
12. The ink jet print head of claim 11, where the displacement
device is one of a piezo-electric operated pump, a piezo-electric
bender, and a bubble chamber.
13. The ink jet print head of claim 1, further including: a second
pressure sensor in the local reservoir to measure pressure in the
local reservoir and to transmit a signal; a transducer firing rate
determiner to identify a rate at which the transducer is firing and
to transmit a rate signal; a controller to receive the signal from
the second pressure sensor and the rate signal from the transducer
firing rate determiner, and to transmit a displacement signal; and
a displacement device to receive the displacement signal and to
displace the local reservoir in or out, via a diaphragm, to
increase or reduce the pressure in the local reservoir.
14. A method to prevent ink starvation in an ink jet print head,
comprising: keeping ink in a primary common reservoir at a high
pressure; detecting, by a pressure sensor in an ink let chamber, a
drop in pressure in the ink let chamber; and transferring the ink
from the primary common reservoir to a local reservoir and the ink
let chamber in response to the drop in pressure in the ink jet
chamber.
15. The method of claim 14, wherein the transferring ink from the
primary common reservoir includes opening a valve between the
primary common reservoir and the local reservoir.
16. The method of claim 15, further including transferring ink from
the local reservoir through the restrictor to the ink jet chamber
to prevent starvation.
17. The method of claim 16, wherein the opening of the valve is
based on a pressure reading from a pressure sensor.
18. The method of claim 17, further including dissipating pressure
in the ink jet chamber by opening a bleed valve.
19. The method of claim 18, wherein dissipating pressure in the ink
jet chamber is based on a pressure reading from a pressure
sensor.
20. The method of claim 14, wherein transferring ink from the
primary common reservoir includes opening a check valve between the
primary common reservoir and the local reservoir.
21. The method of claim 20, further including transferring ink from
the local reservoir through the restrictor to an ink jet
chamber.
22. The method of claim 21, wherein the pressure of the ink being
transferred from the local reservoir through the restrictor to the
ink jet channel is increased or decreased due to a displacement
device displacing in or out of the local reservoir.
23. The method of claim 22, wherein the displacement in or out of
the local reservoir is determined by a pressure sensor located
within the ink jet chamber.
24. An ink jet print head, comprising: an ink jet chamber to
contain ink, the ink jet chamber including an ink droplet ejection
orifice; a restrictor to transfer the ink from a primary reservoir
to the ink jet chamber; a transducer to eject the ink from the ink
jet chamber through the ink droplet ejection orifice; and a
micro-pump, vibrating a diaphragm against the restrictor during
printing operations, to draw the ink from the primary reservoir
into the ink jet chamber.
25. The ink jet print head of claim 24, wherein the micro-pump a
micro-pump transducer to vibrate the diaphragm across the
restrictor to draw the ink from the primary reservoir into the ink
jet chamber.
26. The ink jet print head of claim 25, wherein the micro-pump is
an acoustic pump, the acoustic pump including a piezo-electric
transducer or transducer.
27. The ink jet print head of claim 24, further including a
micro-pump driving device to transmit a signal to the micro-pump to
activate the micro-pump.
28. The ink jet print head of claim 27, wherein the micro-pump
driving device is a resistor-capacitor circuit.
29. The ink jet print head of claim 28, wherein the micro-pump
driving device is a digital circuit.
30. A method to prevent ink starvation in an ink jet print head,
comprising: keeping ink in a primary reservoir; and transferring
the ink from the primary reservoir through a restrictor to an ink
jet chamber by a micro-pump, including a micro-pump transducer,
vibrating a diaphragm over the restrictor.
31. The method of claim 30, further including driving the
micro-pump based on a firing rate of a transducer with a micro-pump
driving device.
32. The method of claim 31, wherein the micro-pump is continuously
activated and a magnitude of a micro-pump pumping action is varied
depending on the firing rate of the transducer.
33. An ink jet printing apparatus, comprising: a paper feed device
to feed paper within the ink jet printing apparatus; and an ink jet
print head, including an ink jet chamber to contain ink, said ink
jet chamber including an ink droplet ejection orifice, a primary
restrictor to transfer the ink from a primary reservoir to the ink
jet chamber, a transducer to eject the ink from the ink jet chamber
through the ink droplet ejection orifice, and a micro-pump,
including a micro-pump transducer, to vibrate a diaphragm across
the restrictor to draw the ink from the primary reservoir into the
ink jet chamber.
34. The ink jet printing apparatus of claim 33, further including a
micro-pump driving device to transmit a signal to the micro-pump to
activate the micro-pump.
35. An ink-jet print head, comprising: an ink jet chamber to
contain ink, said ink jet chamber including an ink droplet ejection
orifice; a secondary common reservoir having a low compliance to
contain the ink at a slightly higher pressure than pressure of the
ink in the ink jet chamber when jetting is taking place; a primary
restrictor to transfer the ink between a primary common reservoir
and the ink jet chamber; and a secondary restrictor to transfer ink
from the secondary common reservoir to the ink jet chamber, wherein
the secondary restrictor has a low resistance and a high
inertance.
36. The ink jet print head of claim 35, wherein the secondary
restrictor is of a circular cross-sectional shape.
37. The ink jet print head of claim 35, further including a
regulated pressure supply to hold constant the pressure of the
secondary common reservoir to keep the compliance of the secondary
common reservoir to enable the secondary common reservoir to
respond to slow variations in the pressure in the ink jet chamber
due to rapid firing of a transducer.
38. The ink jet print head of claim 35, wherein the secondary
common reservoir is small in size.
39. The ink jet print head of claim 35, wherein walls of the
secondary common reservoir are rigid.
40. The ink jet print head of claim 35, wherein a connection
between the secondary common reservoir and the regulated pressure
supply is a high inertance path.
41. A method to prevent ink starvation, comprising: storing ink in
a primary common reservoir and a secondary common reservoir;
transferring the ink from a secondary common reservoir through a
secondary restrictor to an ink jet chamber, wherein the secondary
restrictor is low in resistance and high in inertance.
42. The method of claim 41, further including maintaining a higher
ink pressure in the secondary common reservoir as compared to a
primary ink pressure in the primary common reservoir.
43. The method of claim 42, wherein a regulated pressure supply
maintains the higher ink pressure in the secondary common
reservoir.
44. An ink jet printing apparatus, comprising: a paper feed device
to feed paper within the ink jet printing apparatus; and an ink jet
print head, including an ink jet chamber to contain ink, said ink
jet chamber including an ink droplet ejection orifice, wherein a
transducer ejects ink droplets out of the ink droplet ejection
orifice and onto the paper within the ink jet printing apparatus, a
secondary common reservoir having a low compliance to contain the
ink at a slightly higher pressure than pressure of the ink in the
ink jet chamber when jetting is taking place, a primary restrictor
to transfer ink between a primary common reservoir and the ink jet
chamber, and a secondary restrictor to transfer ink from the
secondary common reservoir to the ink jet chamber, wherein the
secondary restrictor has a low resistance and a high inertance.
45. The ink jet printing apparatus of claim 44, further including a
regulated pressure supply connected by a high inertance path to the
secondary common reservoir to enable the secondary common reservoir
to respond to slow variations in pressure in the ink jet chamber
due to rapid firing of the transducer and not to respond to fast
variations in pressure, the fast pressure utilized to eject the ink
droplets.
46. The ink jet printing apparatus of claim 44, wherein the
secondary restrictor is of a circular cross-sectional shape.
47. An ink-jet punt head, comprising: a single local reservoir,
coupled to a primary common reservoir, to receive ink from the
primary common reservoir, wherein the primary common reservoir
keeps the ink at a high hydrostatic pressure; a single restrictor
passage, coupled to the single local reservoir, to receive the ink
from the single local reservoir and to transfer the ink; a single
ink jet chamber to receive the ink from the single restrictor
passage, said single ink jet chamber including a single ink droplet
ejection orifice; a single ejection device to eject the ink through
the single ink droplet ejection orifice; and a single pressure
sensor located in the ink jet chamber to measure pressure within
the single ink jet chamber during firing of the single ink droplet
ejection device and to transmit a signal.
48. An ink-jet print head, comprising: a plurality of local
reservoirs, said plurality of local reservoirs coupled to a primary
common reservoir, to receive ink from the primary common reservoir,
wherein the primary common reservoir keeps the ink at a high
hydrostatic pressure; a plurality of restrictor passages, said
plurality of restrictor passages coupled to said plurality of local
reservoirs, each restrictor passage receiving the ink from said
corresponding local reservoir and transferring the ink; a plurality
of ink jet chambers coupled to the plurality of restrictor
passages, each of said plurality of ink jet chambers to receive the
ink from the corresponding restrictor passage, and each of said
plurality of ink jet chambers including a ink droplet ejection
orifice; a plurality of ejection devices to eject the ink through
the corresponding plurality of ink droplet ejection orifices; and a
plurality of sensors correspondingly located in the plurality of
the ink jet chambers to measure pressure within the plurality of
ink jet chambers during firing of the plurality of ejection
devices, each of said plurality of sensors transmitting a signal.
Description
BACKGROUND OF THE INVENTION
A. Field of the Invention
This invention relates to improving the performance of ink jet
print heads in high frequency usage conditions.
B. Description of Prior Art
Under high-frequency firing conditions, ink jet print heads
generally experience higher failure rates. There is also a limiting
frequency beyond which the ink jets will not fire. Experiments and
theory have shown that many of these failures occur from continued
motion of the ink in the ink chamber and the ink meniscus of the
orifice after the firing of the print head. When the frequency of
firing becomes higher, the meniscus does not have time to settle
back to equilibrium before the next firing pulse. The motion is
caused by the continued "ringing" associated with resonances in the
ink jet. These resonances include the resonance of the piezo
electric transducer driving element and fluidic resonances in the
ink such as the Helmholtz resonance mode and acoustic modes.
One way to minimize the ringing or resonance of the fluid is to
decrease the size of the restrictor to dampen the Helmholtz
resonance. However, decreasing the size of the restrictor too much
may lead to ink starvation. Starvation failure occurs when the mean
orifice pressure becomes more negative and, when combined with a
transient negative pressure at firing, overcomes the surface
tension strength of the meniscus so that air is drawn into the ink
chamber.
One way to avoid starvation failure is to apply air pressure above
the ink in the reservoir. However, under positive pressure
(hydrostatic head), when the jets are not running, ink starts to
weep out of the orifices. The surface tension of the meniscus tends
to prevent weeping of the ink and the amount of positive pressure
that can be held back depends on the size of the orifices. For the
size of the orifices typically used in ink jet heads, the pressure
cannot be increased beyond about two inches of water when the jets
are not running before the ink starts to weep out of the orifices.
When the jets are started and the frequency increased, the
hydrostatic head can be increased without ink weeping out onto the
outside of the orifice plate. For example, in one experimental
laboratory embodiment, pressure was increased up to +20 inches of
water when the jets were running at 20 kilohertz. (It is common to
refer to the increase or decrease of pressure within the ink jet
chamber as being an increase or decrease in inches of water. In
many cases the density of the ink or other liquid is close to the
density of water so the hydrostatic head is about the same. Other
units of pressure commonly used are the pascal and the bar. One
inch of water is approximately 249 pascals or 2.49.times.10.sup.-3
bars.) In ink jet print heads, the pressure within the ink jet
chamber may be varied by the level of ink or other liquid located
within the ink jet reservoir above or below the level of ink or
other liquid located within the ink jet chamber--i.e. the
hydrostatic "head" of ink. In this embodiment, the use of smaller
restrictors and high positive pressure allowed the running of the
jets up to the piezoelectric driver resonant frequency, which in
this experiment, was 42 kilohertz. Thus, a need exists to allow
high frequency operation of the print head without weeping or ink
starvation.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 illustrates a standard ink jet print head as is available in
the prior art;
FIG. 2 illustrates an ink jet print head according to an embodiment
of the present invention;
FIG. 3 illustrates an ink jet print head including a
pressure-applying device according to an embodiment of the present
invention;
FIG. 4 illustrates an ink jet print head including a micro-pump
device according to an embodiment of the present invention;
FIG. 5 illustrates the principle of the micro-pump action caused by
high frequency pressure fluctuations adopted in an embodiment of
the present invention; and
FIG. 6 illustrates an ink jet print head with a primary common
reservoir and a secondary common reservoir according to an
embodiment of the present invention.
DETAILED DESCRIPTION
The ink jet apparatus may include a print head, an ink jet
reservoir, and other peripheral apparatus. The print head may
include a restrictor member which includes a plurality of
individual restrictors, a chamber member including a plurality of
individual ink jet chambers, and an orifice member including a
plurality of individual ink droplet ejection orifices. The print
head may also include a diaphragm member and a transducer member.
In embodiments of the invention, the ink manifold, the restrictor
member, the chamber member, the orifice member, the diaphragm
member, and the transducer member are configured in plates bonded
together to form the print head. FIG. 1 illustrates a standard ink
jet print head as is available in the prior art. When constructed,
the print head may form plural ink jet devices, each ink jet device
having an orifice 102, an ink jet chamber 104, a restrictor 106, a
diaphragm 108, and a transducer 110. The ink jet print head of the
present invention may dampen meniscus oscillations by using a small
restrictor 106 and overcome ink starvation by applying an increased
hydrostatic pressure to the ink as required. In other embodiments
of the invention, the print head may only include an orifice 102,
an ink jet chamber 104, a restrictor 106, a diaphragm 108, and a
transducer 110.
In one embodiment of the present invention, the ink jet print head
may include a common ink reservoir 112 to contain ink, a restrictor
member including a plurality of individual restrictors 106, a
chamber member including a plurality of ink jet chambers 104, an
orifice member including a plurality of individual ink droplet
ejection orifices 102, a transducer member including a plurality of
transducers 110, a diaphragm member including a plurality of
diaphragms 108, a local reservoir member including a plurality of
local reservoirs (not shown) for containing ink, a plurality of
valves (not shown), a plurality of pressure sensors (not shown),
and a plurality of controllers (not shown). In other embodiments of
the present invention, the ink jet print head may include a
plurality of check valves (not shown). In other embodiments of the
present invention, the ink jet print head may include a
displacement device member including a plurality of displacement
devices(not shown). In embodiments of the invention, the ink jet
print head may include a valve, a bleed valve, a pressure sensor, a
controller, a check valve, and a displacement device.
In an embodiment of the present invention, the common reservoir
member, the restrictor member, the chamber member, the transducer
member, the orifice member, and the diaphragm member are configured
in plates that are bonded together to form the print head.
Additionally, the local reservoir member may be bonded to the
above-mentioned members to form the ink-jet print head. In
additional embodiments, the pressure device member may be bonded to
the above-mentioned members to form the ink jet print head. In
other embodiments of the present invention, the common reservoir
member may not be bonded together with the above-mentioned members
in order to form the ink jet print head.
The invention may be applied in many different applications where a
liquid which is not necessarily an ink, may be jetted from a print
head device. For example, the liquid may be a polymer, a metal, a
plastic, a wax, anything that is a liquid or can be liquefied e.g.
by heating. The above list is only a representative list and should
not be construed as limiting, in that embodiments of the invention
may be applied to any substance that is jetted from a print head
device. In other embodiments of the invention, the ink jet print
head may eject an ultraviolet (UV) radiation curable substance or
other substances which may solidify to form a layer of appreciable
thickness. These substances may be utilized in three-dimensional
modeling. Three-dimensional modeling involves building the model
from many "printed" layers. Hence, three-dimensional modeling
requires many jetted droplets and, therefore, may be a slow
process. High-frequency jetting, described in this invention, may
decrease the time for three-dimensional modeling.
In embodiments of the invention, the ink jet print head may eject
an etching substance in a metered fashion to etch out a printed
circuit board or a semiconductor integrated circuit chip. In other
embodiments of this invention, the ink jet print head may be used
as a micro-metering device for any liquid that needs to be metered
accurately especially in very small quantities. Again, the
above-mentioned embodiments are only representative examples of
uses of an ink jet print head and should not be construed as
limiting. Embodiments of the present invention may be utilized in
any application where a substance is jetted from a print head onto
another surface.
FIG. 2 illustrates an ink jet print head according to an embodiment
of the present invention. When constructed, the print head may form
a plurality of ink jet devices, and each ink jet device 300 may
include an orifice (not shown), an ink jet chamber 308, a
restrictor 306, a diaphragm (not shown), a transducer (not shown),
and a local reservoir 304. In other embodiments, the ink jet print
head may include a single orifice, a single ink jet chamber 308, a
single restrictor 306, a single diaphragm, a single transducer, and
a single local reservoir 304. In embodiments including a plurality
of ink jet devices 300, each of the ink jet devices 300 may include
at least one valve for connecting and disconnecting to a primary
common reservoir 302 and/or for venting the ambient pressure from
the ink jet chamber 308. In an embodiment of the present invention
including a plurality of ink jet devices 300, each of the ink jet
devices 300 may include a displacement device (not shown). Each of
the ink jet devices 300 may operate to selectively eject droplets
of ink from the ink jet chamber 308 through the ink droplet
ejection orifice, in response to the selective energization of the
transducer, which pushes against the diaphragm.
As illustrated in FIG. 2, the primary common reservoir 302 may
define a hollow interior for containing ink for all the plurality
of ink jet devices 300. The primary common reservoir 302 may be
located in the reservoir member (not shown), which may be located
inside the print head. Alternatively, the primary common reservoir
302 may be located outside the print head. The primary common
reservoir 302 may be in flow communication, through the local
reservoir 304 and the restrictor 306, with each ink jet chamber
308. Although a plurality of ink jet devices 300 may exist for in
the ink jet print head, for simplicity, only one is illustrated in
FIG. 2.
In a single ink jet device in an ink jet print head 300, a local
reservoir 304 may receive ink from the primary reservoir 302. In an
embodiment of the invention, the primary reservoir 302 may be
placed at a higher hydrostatic pressure than the local reservoir
304. This configuration may be needed in order to prevent ink
starvation, i.e., not enough ink making it into the ink jet chamber
308. The primary common reservoir 302 may maintain the high
hydrostatic pressure by placing a controllable valve (310 and 312)
between the primary common reservoir 302 and the local reservoir
304. In embodiments of the invention, the controllable value may
include a valve 310 and a bleed valve 312. The controllable valve
may be one physical device or may be two separate valve devices.
The valve 310, when opened or in an open position, may allow the
primary common reservoir 302, which remains at a relatively high
hydrostatic pressure, to increase the pressure in the local
reservoir 304 and adjust it to the pressure needed according to the
printing frequency. The valve 310 may be a piezo-electrically
switched valve.
Illustratively, during a time period that includes the rapid firing
of the transducer, the valve 310 may be opened between the primary
reservoir 302 and the local reservoir 304 allowing the pressure of
the local reservoir 304, and thus the ink jet chamber 308, to
increase. By controlling the pressure in the local reservoir 304 in
this way, the mean pressure in the ink chamber 308 is held
constant. Controlled pressure variations in the local reservoir 304
may compensate for the flow pressure drop across the restrictor
306. After this occurs, the closing of the valve 310 may also
prevent weeping.
The bleed valve 312 may allow the dissipating of pressure from the
local reservoir 304 and hence the ink jet chamber 308 when the
valve 310 is closed. Conversely, when the transducer (not shown) is
not fired or is not fired rapidly, the bleed valve 312 may bleed
off the excess pressure of the ink jet chamber 308 in order to
return the pressure in the ink jet chamber 308 to ambient pressure.
The excess pressure may be bled off or dissipated off from the ink
jet chamber 308. Ink bled off through the bleed valve 312 may be
returned to the primary common reservoir 302 by means of a pump
(not shown).
The opening and closing of the valve 310 and the bleed valve 312
may be determined by a controller 314 and a pressure sensor 316.
The pressure sensor 316 may measure the pressure within the ink jet
chamber 308 and, depending upon the reading, transmit a signal to
the controller 314 to open the valve 310, open the bleed valve 312,
or to open neither valve. For example, if the pressure sensor 316
determines the pressure in the ink jet chamber 308 is low, due to
rapid firing of the transducer, the pressure sensor 316 may
transmit a signal to the controller 314 to open the valve 310 to
allow the higher pressure of the primary common reservoir 302 to be
transferred to the local reservoir 304 and thus the ink jet chamber
308. Conversely, if the pressure sensor 316 determines the pressure
in the ink jet chamber 308 is too high, then the pressure sensor
316 may transmit a signal to the controller 314 instructing it to
open the bleed valve 312.
The primary common reservoir 302 may be placed at high pressure in
a variety of manners. In one embodiment, air may be applied above
the ink by a pressure-applying device (not shown) such as an
elastic membrane. Illustratively, the valve 310 and the bleed valve
312 may be piezo-controlled.
In an alternative embodiment, the pressure sensor (not shown) may
be located in the local reservoir 304. In this embodiment, the
pressure sensor may identify when the pressure has changed within
the local reservoir 304. The pressure sensor may transmit a signal
to the controller 314 to open the valve 310 or to open the bleed
valve 312, as described above. In this embodiment of the invention,
the controller 314 may also need information on the firing rate of
the transducer in order to decide whether to open the valve 310 or
to open the bleed valve 312. A transducer firing rate determiner
(not shown) may identify the firing rate of the transducer. For
example, the transducer firing rate determiner may calculate the
pressure drop across the restrictor 306 from the firing rate of the
transducer and transmit this data to the controller 314. The
pressure sensor may also transmit a signal to the controller 314
indicating the pressure in the local reservoir 304. From these two
signals the controller 314 can compute the mean pressure in the ink
jet chamber 308. In this embodiment, if the computed pressure is
low due to the rapid firing of the transducer, the controller 314
may transmit a valve signal to the valve 310 to open and to the
bleed valve 312 to close, and thus increase the pressure in the
local reservoir 304 and the chamber 308. Conversely, if the
controller 314 computes the pressure in the chamber 308 to be too
high, it may transmit a valve signal to the valve 310 to close and
to the bleed valve 312 to open, thus decreasing the pressure in the
chamber 308.
FIG. 3 illustrates an ink jet print head including a displacement
device according to an embodiment of the present invention. In
another embodiment of the present invention, each ink jet device in
the ink jet print head 400 may include a one-way check valve 404, a
local reservoir 406, a restrictor 407, an ink jet chamber 408, a
pressure sensor 410, a controller 412, and a displacement device
414. In an embodiment of the invention, a common primary reservoir
402 may also be included in the ink jet print head. In this
embodiment, the ink in the primary common reservoir 402 may be
placed at an ambient pressure or a pressure slightly below ambient
pressure. The one-way check valve 404 may allow flow only in the
direction from the primary common reservoir 402 to the local
reservoir 406. In embodiments of the present invention, the
pressure sensor 410 may be located within the ink jet chamber 408.
The pressure sensor 410 may determine the pressure within the ink
jet chamber and transmit a signal to the controller 412 indicating
whether the pressure in ink jet chamber 408 is high or low. The
controller 412 may receive the signal from the pressure sensor 410
and transmit a displacement signal to the displacement device 414
to displace in or out the local reservoir to increase or reduce
pressure within the local reservoir 406.
Illustratively, the displacement device 414 may be a bimorph
device. In another embodiment, the displacement device 414 may be
any type of miniature pump, e.g., a piezo-electric operated pump, a
piezo-electric bender, or a bubble chamber. In an exemplary
embodiment of the present invention, the displacement device 414
may be placed in the local reservoir 406 if the displacement
device's 414 size allows it. The displacement device 414 may press
in on the secondary reservoir 406 if high pressure in the ink jet
chamber 408 is needed because the pressure sensor 410 determined
the pressure in the ink jet chamber 408 was too low. For example,
the displacement device 414 may be activated at the same time the
transducer is fired, slightly before the transducer is fired, or
slightly after the transducer is fired.
Illustratively, if an increase in pressure is desired in the ink
jet chamber 408, the displacement device 414 or a foot assembly
(not shown) pushed by the displacement device 414 may press against
a diaphragm (not shown) in an area corresponding to the local
reservoir 406. The pushing of the displacement device 414 may
depress the diaphragm, slightly decrease the size of the local
reservoir 406, and thereby increase the hydrostatic pressure in the
local reservoir 406. The pressure applied by the displacement
device 414 in the local reservoir 406 may be at a level
significantly lower than the instantaneous pressure applied by the
piezo-electric driving transducer in the ink jet chamber 408
(generally around the level of 5-10 mm of water compared to a level
of 1 atmosphere, i.e., several orders of magnitude lower). As
discussed previously, the maintenance of the higher pressure in the
local reservoir 406 may prevent ink starvation during a timeframe
including when the transducer is firing.
In another embodiment of the present invention, the pressure sensor
410 may be located within the local reservoir 406. The pressure
sensor 410 may determine the pressure in the local reservoir 406.
The pressure sensor 410 may generate a signal and transmit the
signal to a controller 412, which in turn transmits the
displacement signal to the displacement device 414. The controller
412 may also receive a signal transmitted from a transducer firing
rate determiner (not shown) in the ink jet chamber 408 indicating
the rate of firing of the transducer. The firing rate determines
the rate of ink flow through the restrictor 407 and hence the
pressure drop across the restrictor 407. With the signal from the
pressure sensor 410 and the signal from the transducer, the
controller 412 may thus be able to compute the pressure in the ink
jet chamber 408. Illustratively, if the controller 412 receives a
rate signal that the transducer has been fired rapidly and if the
controller 412 also receives a signal that the pressure of the ink
in the local reservoir is low from the pressure sensor, the
controller 412 may compute that the pressure in the ink jet chamber
408 is low and transmit a signal to the displacement device 414 to
depress either the diaphragm or the foot to reduce the size of the
local reservoir 406 and increase the flow, and thus pressure, in
the local reservoir 406, the restrictor 407, and the ink jet
chamber 408.
FIG. 4 illustrates an ink jet print head including a micro-pump
device according to an embodiment of the present invention. In an
embodiment of the present invention, the restrictor member, the
chamber member, the transducer member, the orifice member, the
diaphragm member, and the reservoir member may be configured in
plates that are bonded together to form a print head. When
constructed, the print head 500 may form a plurality of ink jet
devices, with each ink jet device having an orifice 514, an ink jet
chamber 512, a restrictor 510, a diaphragm 508, a transducer 506, a
micro-pump 504, and a micro-pump driving device 502. In other
embodiments of the invention, the print head may include a single
orifice 514, a single ink jet chamber 512, a single restrictor 510,
a single diaphragm 508, a single transducer 506, a single
micro-pump 504, and a single micro-pump pumping device 502. The
micro-pump 504 may include a micro-pump transducer 530 and a
micro-pump immersed nozzle 532. The ink jet print head may also
include a primary reservoir 501. As noted previously, the ink jet
print head 500 operates to selectively eject droplets of ink from
the ink jet chamber 512 through the orifice 514, in response to the
selective energization of the transducer 506.
The micro-pump driving device 502 may energize the micro-pump 504.
The micro-pump 504 may be any type of pump that can be made small
enough to pump ink through the restrictor 510. In one embodiment,
the micro-pump 504 may be an acoustic pump, also referred to as an
ultrasonic pump. The acoustic micro-pump 504 may comprise a
piezo-electric transducer 530 attached to the diaphragm 508 and an
immersed nozzle 532. In this embodiment, the micro-pump transducer
530 vibrates the diaphragm 508. By the micro-pump 504 vibrating the
diaphragm 508, the diaphragm 508 may act upon the restrictor 510 in
the presence of an immersed nozzle or choke 532, to create a
pumping action. FIG. 5 illustrates the principle of an acoustic
micro-pump vibration according to an embodiment of the present
invention. In FIG. 5, an acoustic micro-pump is illustrated
comprising a cylindrical piezo-electric transducer 610, which is
disposed over a flexible thin tube 604 connected to a tube with an
immersed and tapered nozzle 606. As the cylindrical piezo-electric
transducer 610 is vibrated against the tube 604, the liquid is
drawn through the immersed nozzle 606 through the tube 604 in the
direction of the arrow.
Illustratively, the micro-pumping action of the micro-pump 504 may
result from the micro-pump transducer 530 vibrating the diaphragm
508 against the restrictor 510, which in the presence of the
immersed nozzle 532, may draw more ink from the primary reservoir
501 into the ink jet chamber 512. The addition of more ink into the
ink jet chamber 512 may maintain the hydrostatic pressure within
the ink jet chamber 512. The pressure created by the micro-pump 504
may be several orders of magnitude of pressure below the pressure
applied by the transducer 506. However, generally, the small
pressure created by the micro-pump 504 may be generated over a time
period much longer than the duration of the pressure applied by the
transducer 506.
The micro-pump 504 activation may be triggered in conjunction with
the firing of the transducer 506. In one embodiment, the micro-pump
504 activation may be initiated each time the transducer 506 is
fired. In this embodiment, the micro-pump 504 activation may be
initiated at the same time the transducer 506 is fired, in advance
of the transducer 506 firing, or after the transducer 506 has been
fired. In another embodiment of the present invention, the
micro-pump 504 may be activated after a certain number of
transducer 506 firings. For example, the micro-pump 504 may be
activated once for every three-transducer 506 firings. Conversely,
the micro-pump 504 may be activated a specified number of times for
each transducer firing, e.g., micro-pump 504 activated four times
for each transducer 506 firing. In another embodiment, the duration
of activation of the micro-pump 504 may be made dependent upon the
rate of transducer 506 firings.
In an alternative embodiment of the present invention, the
micro-pump 504 may continuously be activated, but the magnitude of
the pumping action of the micro-pump 504 when the micro-pump 504 is
activated may be varied depending on the frequency of the
transducer 506 firing. Illustratively, if the transducer 506 fires
four times, the magnitude of the pumping action of the micro-pump
504 may be greater by a predetermined factor than the magnitude of
the micro-pump 504 pumping action if the transducer 506 was only
fired one time. The increased magnitude of the micro-pump 504
pumping action may maintain the desired hydrostatic pressure within
the ink jet chamber 512, which may prevent ink starvation.
In one embodiment of the present invention, the micro-pump driving
device 502 may be an analog circuit which provides an output signal
that corresponds to the frequency of transducer 506 firings. The
micro-pump 504 may be activated after a certain output signal level
is reached. For example, a simple resistor-capacitor (RC) circuit
may be utilized as a micro-pump driving device 502. Each transducer
506 drive pulse may charge a capacitor in the RC circuit, in which
the charge slowly leaks away over time. The voltage across the
resistor in the RC circuit may increase with an increased number of
transducer 506 drive pulses, i.e., an increased number of
transducer 506 firings. If fewer drive pulses occur, the voltage
across the resistor in the RC circuit may be smaller. The
activation of the micro-pump 504 may be determined based on the
voltage level across the resistor in the RC circuit. If the voltage
level is higher than a specific threshold, indicating more frequent
firing of the transducer 506, the micro-pump 504 may be activated
or activated with a higher pumping action. Conversely, if the
voltage level is low, indicating less frequent firing of the
transducer 506, the micro-pump 504 may not be activated until the
voltage level meets a threshold or may be activated with a
decreased pumping action.
In an alternative embodiment, the micro-pump driving device 502 may
be a digital circuit that outputs a signal to drive the activation
of the micro-pump 504. The digital circuit may accept an input
signal identifying that the transducer 506 has been fired. The
digital circuit may include software or circuitry for an algorithm
that determines when the micro-pump 504 may be activated or how
energetically the micro-pump 504 may be activated. For example, as
discussed previously, the software or circuitry may identify that
the micro-pump 504 should be activated for every two firings of the
transducer 506 or it may define a curve, or non-linear
relationship, of micro-pump 504 pumping activity versus frequency.
Once the software or circuitry determines when or how energetically
the micro-pump 504 should be activated, an output signal is
generated and sent to the micro-pump 504 to initiate or control
activation.
In another embodiment of the present invention, a primary
restrictor member, a secondary restrictor member, the chamber
member, the transducer member, the orifice member, the diaphragm
member, a primary reservoir member, and a secondary reservoir
member are configured in plates that are bonded together to form a
print head. In one embodiment of the invention, the primary
reservoir member and the secondary reservoir member are configured
in one plate. In another embodiment of the invention, the primary
reservoir member and the secondary reservoir member may be
configured in separate plates. In addition, in an embodiment
including a separate plate for a primary reservoir member and a
secondary reservoir member, the secondary restrictor member may
require a separate restrictor plate.
FIG. 6 illustrates an ink jet print head with a primary common
reservoir and a secondary common reservoir according to an
embodiment of the present invention. When constructed, the print
head 700 forms a plurality of ink jet devices, with each ink jet
device having an orifice (not shown), an ink jet chamber 702, a
primary restrictor 704, a secondary restrictor 706, a diaphragm
(not shown), and a transducer (not shown). A primary common
reservoir and a secondary common reservoir may be utilized by all
of the plurality of ink jet devices. In other embodiments of the
present invention, the print head 700 may include a single orifice,
a single ink jet chamber 702, a single primary restrictor 704, a
single secondary restrictor 706, a single secondary common
reservoir 708, a single diaphragm, and a single transducer. In
embodiments of the invention including a plurality of ink jet
devices, the ink jet print head 700 may also include a primary
common reservoir 710. As noted previously, each of the plurality of
ink jet devices in the ink jet print head 700 operates to
selectively eject droplets of ink from the ink jet chamber 702
through the ink droplet ejection orifice, in response to the
selective energization of the transducer.
In this embodiment of the invention, the ink jet chamber 702 may
receive ink from a secondary common reservoir 708 through the
secondary restrictor 706 along with receiving ink from the primary
common reservoir 710 through the first restrictor 704. The primary
common reservoir 710 may be a large container maintained at/open to
an ambient atmospheric pressure. The goal of this embodiment of the
invention is to keep the pressure of the ink in the ink jet chamber
702 at a constant, somewhat higher than normal pressure level,
during time periods when the transducer is firing in order to
eliminate starvation. The secondary common reservoir 708 may be
kept at a constant pressure almost equal to the pressure of the ink
in the ink jet chamber 702. It may be at a very slightly higher
pressure because of the pressure drop due to the ink flow through
the secondary restrictor 706. By making the resistance of the
secondary restrictor 706 relatively small, the pressure difference
can be made negligibly small. The secondary common reservoir 708
may be made relatively as small with rigid walls so that the
secondary common reservoir's 708 compliance is small. It may be
kept at a constant pressure by a movable, massive, rigid wall, such
as a piston 714, and a regulated pressure supply 712. A relatively
massive movable wall or massive piston 714 may add equivalent
fluidic inertance between the secondary common reservoir 708 and
the regulated pressure supply 712. In an embodiment of the present
invention, the regulated pressure supply 712 may be part of the
print head 700. In other embodiments of the present invention, the
regulated pressure supply 712 may not be part of the print
head.
The secondary common reservoir 708 may supply a large portion of
the ink required by the ink jet chamber 702. At higher transducer
firing frequencies, the pressure drop, i.e., pressure drop is equal
to flow rate times resistance, across the secondary restrictor 706
may be much smaller than the pressure drop across the primary
restrictor 704 because the resistance in the secondary restrictor
706 may be much smaller than the resistance in the primary
restrictor 704.
The secondary restrictor 706 may have a very low resistance but a
very high inertance. This configuration may be required so that the
secondary reservoir 708 and the secondary restrictor 706 have a
high impedance to rapid pressure fluctuations in the ink jet
chamber 702, which occur when the transducer is fired. To further
increase the impedance to rapid pressure fluctuations, the
compliance of the secondary restrictor 706 may be made to be small.
In other words, the ink within the secondary reservoir 708 may move
through the secondary restrictor 706 very easily under the
influence of a steady pressure but may not move very easily in
response to rapid pressure fluctuations because of the high
inertance of the secondary restrictor 706 and the small compliance
of the secondary reservoir 708. Additionally, the high equivalent
fluidic inertance between the secondary reservoir 708 and the
regulated pressure supply 712, may serve to isolate the secondary
reservoir 708 from any high compliance of the regulated pressure
supply 712. Illustratively, the secondary reservoir 708 and the
secondary restrictor 706 may look like a high impedance path to the
rapid fluctuations. Most of the flow resulting from rapid pressure
fluctuations occurs through the primary restrictor 704 and is
controlled essentially by the primary restrictor 704 and the high
compliance of the primary reservoir 710.
The secondary restrictor 706 may have a cross-sectional shape,
which has a low resistance and a high inertance. In an exemplary
embodiment of the present invention, the second restrictor 706 may
be of a circular cross-sectional shape. In embodiments of the
invention, more inertance may be desirable and the second common
reservoir 708 may be established as a pressure regulated reservoir
with a small compliance. A regulated pressure supply 712 may be
used to hold the pressure in the chamber 702 at an almost constant
value for steady or low frequency pressure fluctuations. High
frequency pressure changes may occur within the ink jet chamber 702
and may be controlled primarily by the compliance of the ink jet
chamber 702, the resistance and inertance of the primary restrictor
704, and the very large compliance of the primary reservoir 710.
The high frequency pressure fluctuations may occur in a time of
about one to twenty microseconds. Large pressure variations may
occur in this time scale in the ink jet chamber 702. Slower changes
occurring in times of greater than two to twenty milliseconds may
be absorbed by the slow responding regulated pressure supply 712.
In embodiments of the invention, walls of the secondary reservoir
708 which are not in pressure communication with the regulated
pressure supply 712 may need to be rigid. In embodiments of the
invention, the secondary reservoir 708 may need to be small. In
this embodiment of the invention, a relatively massive flexible
wall of the secondary reservoir 708 may be used for pressure
communication between the regulated pressure supply 712 and the
secondary reservoir 708. In embodiments of the invention, a massive
piston 714 may be used for pressure communication between the
regulated pressure supply 712 and the secondary reservoir 708.
In another embodiment of the present invention, the primary
restrictor 704 resistance may be increased to above current levels
to improve the damping of the meniscus. Ink that is consumed by the
jetting process may come almost entirely from the secondary common
reservoir 708. It may even be desirable to hold the primary
reservoir 710 at a pressure very slightly lower than that of the
secondary reservoir 708. In this case, a steady flow of ink may
occur from the secondary common reservoir 708 to the first common
reservoir 710 even when no jetting is taking place. An ink return
device (not shown) may need to transfer the ink from the first
common reservoir 710 to the second common reservoir 708.
While the description above refers to particular embodiments of the
present invention, it should be readily apparent to people of
ordinary skill in the art that a number of modifications may be
made without departing from the spirit thereof The accompanying
claims are intended to cover such modifications as would fall
within the true spirit and scope of the invention. The presently
disclosed embodiments are, therefore, to be considered in all
respects as illustrative and not restrictive, the scope of the
invention being indicated by the appended claims rather than the
foregoing description. All changes that come within the meaning of
and range of equivalency of the claims are intended to be embraced
therein.
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